High precision pressure sensors employ quartz thickness shear resonators.  The frequencies of these vary not only with pressure, but also with temperature.  Temperature control, or compensation is used to minimize the errors due to temperature effects.  Some pressure sensors have used a temperature sensor that is external, but in close proximity, to the pressure sensing resonator, and shielded from the applied pressure.  However, when a temperature gradient exists between the pressure and temperature sensors, such as may occur under pressure and temperature transients, the accuracy of pressure measurement is degraded.
	Dual-mode pressure sensors have been proposed in which the b-mode is stress compensated and the c-mode is temperature compensated.  In such a sensor, the b-mode indicates primarily the temperature of the sensing resonator, and the c-mode indicates the applied pressure. As the b-mode’s frequency depends on the temperature of the resonator’s vibrating volume, the effects of temperature gradients are greatly reduced.  Under pressure transients, especially, dual-mode pressure sensors allow for superior temperature sensing and compensation accuracy, and superior pressure sensing accuracy.  The above diagram shows such a dual mode pressure sensor.
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	R. J. Besson, J. J. Boy, B. Glotin, Y. Jinzaki, B. Sinha, and M. Valdois, “A dual-mode thickness-shear quartz pressure sensor,” IEEE Trans. Ultrason. Ferroelect. Freq. Contr., Vol. 40, pp. 584-591, 1993.
	N. Matsumoto, Y. Sudo, B. Sinha and M. Niwa, “Long-term stability and performance characteristics of crystal gauge at high pressures and temperatures,” Proc. 1999 IEEE Int’l Frequency Control Symp.